BY E. C. ANDREWS. 555 



Heer's and Unger's determinations of genera upon the evidence of 

 leaves alone.* 



Another strong reason for not accepting the statement that 

 Eucalyptus flourished in the Northern Hemisphere during the Cre- 

 taceous and Tertiary, is to be found by observations of the juvenile 

 leaves of the genus. The obstinate persistence of juvenile oppo- 

 site, cordate, sessile, and horizontal leaves in the genus, indicates 

 that such leaf-types had been thoroughly well established for a 

 very long period, in the family, before the evolution of the genus 

 Eucalyptus; and that the later, typical Eucalyptus-leaf, with 

 twisted stalk, is a more unstable adaptation to a harsher climate, 

 and one which would tend to become extinct, in favour of the old 

 persistent type, under certain favourable climatic conditions. But 

 it is exactly the later, more or less xerophytic and unstable form, 

 which has been always reported as existing in the Cretaceous and 

 Tertiary beds of the Northern Hemisphere, beds strongly sugges- 

 tive of moist genial climates; and, moreover, even so, as Deanefhas 

 pointed out, such leaves recorded as Eucalypts, might equally be 

 made to fit the plants of other families. Furthermore, such 

 recorded leaves would not be regarded, by a student of Australian 

 Eucalypts, as being suggestive of even the adult Eucalyptus-leaf 

 of later xerophytic origin. 



The existence of several distinct groups of Eucalypts, in regions 

 partly overlapping, is very instructive in any discussion as to the 

 origin of the Eucalypts. Indeed, a careful examination of this 

 genus would serve well as a guide to the methods employed by 

 the Myrtaceae in the development of the endemic types of Aus- 

 tralasia. The group which presents the most striking morpholo- 

 gical similarities to the generalised type of the Myrtaceae, includes 



* Island Life. p. 486. 

 t " Observations on Tertiary Flora of Australia." These Proceedings, 

 1900, pp. 463-475. Deane, however, suggests that the capsular-fruited 

 Myrtaceje originated in Northern or North-eastern Australia, then attained 

 their maximum development in Western Australia, and gave rise to the 

 fleshy fruited Myrtaceae, which later spread to Asia and Europe, as differ- 

 entiations of the primitive capsular type {ibid., p. 474). 



